In recent years, resource conservation, environmental measures, etc. have been emphasized. Along with this, there have been increasingly stronger calls for lower fuel consumption of vehicles. For the automobile tires, it is demanded to contribute for lower fuel consumption, by making the rolling resistance smaller. To make the rolling resistance of tires smaller, in general a rubber material which can give vulcanized rubber with a low heat buildup is used as the rubber material for the tires.
As the rubber for tire, in general, a conjugated diene rubber such as natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber has been used. In recent years, it is been proposed to lower the heat buildup property by using a conjugated diene rubber in which a substituent with affinity with the silica used as a filler is introduced to the polymer chain end.
On the other hand, in a cycloolefin rubber obtained by ring-opening metathesis polymerization of a cycloolefin such as cyclopentene, by adding an olefin compound having a substituent with affinity with silica at the time of polymerization it is possible to easily introduce the substituent to its end. For example, Patent Documents 1 to 3 propose a method of introducing an alkoxysilyl group to a polymer chain end of cyclopentene rubber. It is known that by introducing an alkoxysilyl group, rubber for tire excellent in low fuel consumption and abrasion resistance is obtained. However, according to studies of the present inventors, there are problems that depending on manufacturing conditions or storage conditions, cycloolefin rubber alkoxylated at the polymer chain end ends up forming ingredients not dissolving in general organic solvents after recovery by the usual recovery method of steam stripping or after long term storage and cannot be blended or kneaded due to this and that even after forming and vulcanization, the tire properties deteriorate and the demand for low fuel consumption cannot be met.